: Approximately 7 percent of named couples in the U.S. report difficulty in achieving a pregnancy. Although male factor accounts for 50 percent of these cases, the etiology of the majority of the cases of male infertility is unknown. Many scientists have proposed that a major etiology of idiopathic infertility may be exposure(s) to environmental chemicals that disrupt male reproduction We hypothesize that parameters measured by a semen analysis may be influenced by environmental conditions, specifically air quality and ambient temperature. The specific aims are to determine if semen quality is related to changes in ambient air quality and/or temperature by: 1) correlating changes in semen analyses with reported changes in air pollutants and toxicants and ambient temperature over a period of one year, during two different decades, and in two separate geographical locations. 2) Comparing the observed changes between the two time points to examine the effects of changing levels of pollution on sperm parameters. 3) Comparing the observed changes between the two locations to examine the geographic differences between the mean semen analysis values and their changes over time. Semen analysis data from fertile sperm donors who have collected repeated semen samples over at least a 12-month period will be evaluated. Changes in sperm parameters will be correlated with air quality data, toxics data, and ambient daily temperature.